Book/Dissertation / PhD Thesis

FZJ-2018-02951

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Ion beam treatment of functional layers in thin-film silicon solar cells

Zhang, W. (Corresponding author)FZJ*

2013
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-864-8

Please use a persistent id in citations: http://hdl.handle.net/2128/18498

Abstract: In silicon thin-film solar cells, transparent conductive layers have to fulfill the followingrequirements: high conductivity as effective contact, high transparency to transmit thelight into the cell, and a textured surface which provides light scattering. Magnetronsputtered and wet-chemically textured aluminum doped zinc oxide (ZnO:Al) films arewidely used as the transparent conductor. The technological goal of this dissertation isto develop an alternative to the wet etching process for light trapping in the thin siliconabsorber layers through modification of the glass/ZnO:Al or ZnO:Al/Si interfaces byion beam treatment. The study focuses on the textured growth of ZnO:Al films on ionbeam pretreated glass substrates, and the preparation and application of textured glassfor light trapping.The technological aspects such as the etch rates of the glass substrate and ZnO:Alfilms with different ion beam configurations were studied. The experimental etch ratesare compared with simulated and theoretically predicted values. With regard to the ionbeam treatment of glass substrate, the influence of the ion pretreated glass on the growthof ZnO:Al films was investigated. The ZnO:Al films grown on ion beam pretreatedglass substrates exhibit self-textured morphology with surface roughness of 40 nm whileremaining highly conductive. Silicon thin-film solar cells prepared on the as-grown roughZnO:Al films show that this front contact can provide excellent light trapping effect.The highest initial efficiencies for amorphous single junction solar cells on as-grownrough ZnO:Al films was 9.4 %. The as-grown rough morphology was attributed to largeconical ZnO:Al grains initiated from the ion pretreated glass surface. It was found thatthe roughness of the as-grown rough ZnO:Al film is proportional to the number of Odangling bonds created by ion beam treatment on the glass substrate. A growth modelwas proposed to explain the growth mechanism of ZnO:Al films on Zn- and O-polar ZnOsingle crystals, as well as on untreated and ion beam treated glass substrates.With regard to the ion beam treatment of ZnO:Al films, the influence of the iontreatment on the surface morphology, HCl etching, silicon growth, and additional ZnO:Algrowth was investigated. Ion beam etching has a smoothening effect on the texturedZnO:Al films. Using sputtered and wet chemically etched ZnO:Al as ion beam etchingmask, textured glass with features similar to the ZnO:Al films were obtained. Texturedglass with a wide range of morphologies was prepared by varying the etching mask andthe ion beam treatment conditions. Finally, as-grown textured ZnO:Al films prepared onion beam treated textured glass, which exhibit ’double textured’ features, were producedand applied in solar cells.The ion beam treatment enabled the preparation of light scattering surfaces by texturedglass and as-grown rough ZnO:Al films without the need of wet etching betweenTCO preparation and absorber deposition. Further, new ’double textured’ surface structurescould be created by the combination of both techniques. Solar cells with efficiencyof 11.9 % proved the applicability as-grown textured ZnO:Al for light trapping. Thegrowth studies provided deeper insights and a new understanding of ZnO structure formationand will govern optimization of ZnO:Al film properties.

Keyword(s): Solarzelle

Note: RWTH Aachen, Diss., 2012

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Contributing Institute(s):

1. Photovoltaik (IEK-5)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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Database coverage:

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